Fans of this kind are known and until now were constructed in such a way that the inside of the housing is shaped in a spiral form so that the end of the spiral with the greatest distance from the middle axis of the impeller is arranged in the neighbourhood of the outlet.
If the housing consists of a single thin wall, which of course reduces its costs of manufacturing from iron sheets, the outside of these centrifugal fans is also shaped in a spiral form.
These known centrifugal fans have the disadvantage that they cannot be mounted easily in an arbitrary position but rather require additional auxiliary means for this.
Accordingly, a known centrifugal fan, the housing of which is shaped in a spiral form from iron sheets, is provided for instance with rectangular walls or plates at its two front walls, said walls or plates standing out from the spiral shaped housing, and then can be mounted by means of these plates in more than one position. The mounting of the above-mentioned plates at the front sides of the known centrifugal fan however requires an increased amount of material and work which increases the price also.
The problem underlying the invention consists in manufacturing a centrifugal fan of the kind described at the very beginning in a simple and inexpensive way from iron sheets and thereby to provide a centrifugal fan not only with an inner form which is aerodynamically acceptable but also with an outer form which allows its mounting in different positions.